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WBCS Preliminary Examination 2019 — General Studies · Question 161 of 200

Q161
ReasoningSeating Arrangement, Ranking & Puzzles
In the following series, how many such odd numbers are there which are divisible by 3 or 5, then followed by odd numbers, and then also followed by even numbers?
  1. a.Zero
  2. b.One
  3. c.Two
  4. d.Three

Answer: (C) Two

Scanning the sequence in overlapping triplets, exactly two starting numbers satisfy all three conditions (odd, divisible by 3 or 5, immediately followed by an odd number, which is in turn immediately followed by an even number): the triplet 3-25-18 and the triplet 21-45-46, giving two qualifying cases.